/Engine/Source/Runtime/Core/Public/GenericPlatform/GenericPlatformMisc.h
Get (or create) the unique ID used to identify this computer. This is sort of a misnomer, as there will actually be one per user account on the operating system. This is NOT based on a machine fingerprint.
static [FGuid](API\Runtime\Core\Misc\FGuid) GetMachineId()